The present disclosure relates generally to storage rack systems for articles loaded onto the type of pallets that are typically adapted to be handled by fork lift trucks and, more particularly, to storage rack systems of the push-back type, wherein a pallet of goods is loaded on a cart and a second pallet of goods is used to push the first pallet on the cart from the front of the storage rack to the back of the rack, to make room for the second pallet of goods, and so on.
Storage systems are used in warehouses, department stores, cold storage areas and other storage facilities to store pallets loaded with different goods. Certain storage systems employ extensive multi-story storage rack systems, often called deep rack or high-density storage systems, to store large amounts of a variety of different products.
Push-back storage systems are known in the art. A two deep system has been in use since the late 1950's. Three-deep and four-deep systems are described in U.S. Pat. No. 4,955,489, incorporated herein by reference. U.S. Pat. No. 4,949,852, incorporated herein by reference, describes a three-deep and four-deep system having a double cart assembly, wherein a large cart rides on the tracks and a smaller cart is carried by and movably mounted on the larger cart. See also U.S. Pat. Nos. 4,341,313 and 4,773,546, also incorporated herein by reference. U.S. Pat. No. 5,328,038, incorporated by reference, describes a system for storing eight pallets or more in a single row.
Rack systems are typically formed with vertical columns, which support horizontal rails running lengthwise from the front of a row to the back of each row. The horizontal rails can have the structure of an I-beam, having a lower horizontal wall, a vertical wall extending up from the lower wall and an upper horizontal wall at the top of the vertical wall. The rails are typically parallel. The portion of the upper or lower horizontal wall that faces the corresponding rail of a storage row can be referred to as the inner horizontal walls and the horizontal walls that face away from the corresponding rail can be referred to as the outer horizontal walls. The wheels of the carts that support the pallets can ride on the upper surface of the inner or outer lower horizontal wall of the horizontal rails.
Carts for supporting pallets commonly have a rectangular upper support portion on which the pallet rests and four legs extending downward from the front and rear corners of the support portion. The lower ends of the legs each support a wheel. If a wheel faces outward, it should ride on the inside flange of the lower wall, inside of the vertical wall. If it faces inward, it should ride on the outer flange, outside of the vertical wall. The distance between the upper surface of the support portion of the cart and the wheel determines the height the cart rides above the horizontal rail.
A crossbar typically extends sideways between the vertical columns, across the front of a pallet storage row, in front of the left horizontal rail and the right horizontal rail (left and right are from the perspective of looking into the row). This crossbar blocks the cart wheels from rolling out of the row. It also blocks access to the upper surfaces of the lower walls of the horizontal rails when it is desired to load a cart onto the row. Therefore, there was no easy way to mount the pallet cart wheels on the lower wall of the horizontal rails.
In order to provide access for the wheels, a pair of cut-out notches or slots is commonly formed in the inner and/or outer flange of the upper horizontal wall of the left or right horizontal rail. These notches are spaced a uniform distance from each other to match the wheel spacing between the front and rear wheels of a pallet cart. Therefore, the front to back wheel spacing of all the carts is often standardized to match the standardized spacing of the notches.
To install the carts on the rack, the side of the cart facing the notches is raised to tilt the cart sideways. A front/rear pair of wheels are placed on the upper surface of the lower wall of the rail without the cut-out slots. The front/rear pair of wheels on the other side of the cart are then lowered through the pair of slots, onto the upper surface of the lower wall. At this point, the cart is flat, with all four wheels on the upper surface of the lower wall.
The carts are often approximately 100 pounds in weight. It has therefore been difficult, especially as racks have increased in height, to fit the wheels on one side of the cart into the un-notched rails, then slide the wheels on the other side into the notches.
Other difficulties exist. In order to nest the carts, the front and rear wheels ride on opposite sides of the vertical wall. A rear cart, with inwardly facing front wheels on legs on the outside of the rail can slide over a front cart with its rear wheels facing outward on legs on the inside of the left and right rails. That way, a rear cart can slide over a front cart, until the front of the front legs of the rear cart contact the rear of the front legs of the front cart. Each successive cart became recessed from the previous cart, based on the width of the leg holding the uniformly spaced cart wheels. Therefore, in a multi-cart system, the rear-most (upper) cart can become undesirably recessed from the front of the rack.
These and other problems have persisted for many years without satisfactory solution. Accordingly, a more satisfactory structure, system and method are needed to overcome drawbacks and deficiencies in the prior art.